After accepting the contract, the assassination contract skull marker will appear on the map within a square-shaped restricted area zone in a small market square directly northeast of our current position.
Run over to the target area and approach it from the south. Hire some dancers here to lure the guards away from the guard position at the south entrance. As they leave, move inside and quickly climb the wooden beam between the cannons to your right. From the end of this, jump into the trees nearby.
Use Eagle Vision to identify your target and when he walks below you, perform an air assassination on him to fulfil the contract.